In a polymer electrolyte fuel cell, a device for humidifying and supplying a fuel gas such as hydrogen, etc., and an oxidizer gas such as oxygen, etc. (hereinafter both are called a reaction gas) is required.
For example, a device utilizing a hollow fiber membrane as disclosed in JP-A-8-273687 is known as such a humidifier.
The humidifier in the conventional art will be explained by reference to FIG. 5. FIG. 5 is a schematically sectional view of the humidifier in the conventional art.
As shown in this figure, the humidifier 100 in the conventional art consists schematically of a case 101 and a hollow fiber membrane bundle 102 filled within this case 101.
The case 101 is approximately formed in a cylindrical shape, and has an opening portion 101a at one end of the cylinder and an opening portion 101b at the other end. Further, the case 101 has opening portions 101c, 101d on its sidewall.
And, the hollow fiber membrane bundle 102 is filled within this case 101. One end of the hollow fiber membrane bundle 102 is sealed between the outer wall faces of the hollow fiber membranes and between the outer wall faces of the hollow fiber membranes and the inner wall face of the case 101 so as to open only the hollow interior in the opening portion 101a. The other end of the hollow fiber membrane bundle 102 is similarly sealed between the outer wall faces of the hollow fiber membranes and between the outer wall faces of the hollow fiber membranes and the inner wall face of the case 101 so as to open only the hollow interior in the opening portion 101b. 
Also, a clearance 103 is arranged on the side face side of the hollow fiber membrane bundle 102 between the hollow fiber membrane bundle 102 and the case 101.
Thus, a first path entering the hollow interior of the hollow fiber membrane of the hollow fiber membrane bundle 102 from the opening portion 101a side (arrow S0), and reaching the other end side of the hollow fiber membrane bundle 102 through the hollow interior (arrow S1) is arranged. Further, a second path entering the interior of the case 101 from the opening portion 101d (arrow T0), and reaching the exterior of the case 101 from the opening portion 101c through the clearance 103 is arranged.
Thus, for example, the reaction gas is flowed to the first path and water is flowed to the second path so that the reaction gas within the first path is humidified by transmitting the water within the second path through the membrane of the hollow fiber membrane and diffusing this water into the first path.
Since the humidifier is constructed so as to perform a humidifying action by utilizing that water is transmitted through the membrane of the hollow fiber membrane in this way, the humidifying action is accelerated as the area of the flowing water coming in contact with the hollow fiber membrane is increased.
However, in the above conventional art, since the construction for setting plural hollow fiber membranes to a columnar bundle and flowing water onto its outer circumferential wall face is used, the water is flowed onto the outer circumferential surface of the bundle along the axial line. Thus, there are defects in that no water is sufficiently permeated to the interior of the bundle, and no hollow fiber membrane near the center of the bundle effectively functions, and humidifying efficiency is low.
An object of the present invention is to provide a humidifier for improving the humidifying efficiency.